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J. Perelman
"Entertaining physics". Book 1.
Chapter 2. Gravity and weight. A lever. Pressure


What you are doing tens of thousands of times a day throughout your life, you should be well aware of. So people think, but this is not always true. The best example is walking and running. Is there anything more familiar than these movements? And are there many people who have a clear idea of how, in fact, we move your body when walking and running and how different these two kinds of movements? Listen, that speaks of walking and running physiology [the Text of the passage is taken from “Lectures on Zoology” professional Fields Bera; illustrations added by the compiler.]. For most, I am sure, this description will be brand new.

“Suppose a man stands on one leg, for example, on the right. Imagine that, he lifts the heel, tilting at the same time the torso forward (walking man, starting from the support, it has an extension to the weight pressure of about 20 kg of Here, by the way, it follows that the walking man stronger pressure on the ground than standing. - J. P.).

As a person walks. Successive positions of the body during walking.

In this position, the perpendicular from the centre of gravity, of course, will come from the area of the base of support, and people should fall forward. But barely begins this fall, as his left leg, remaining in the air quickly moves forward and becomes the ground in front of the perpendicular from the centre of gravity, so that the latter, i.e., the perpendicular falls within the square formed by the lines that connect points of support of both legs. The balance is thus restored; man stepped out, took a step.

The graphical representation of the movements of the legs during walking. The top line (A) refers to one leg, the lower (In) - to another. Straight lines correspond to the points of support on the ground, arc - motion moments of feet without support. From the graph it is seen that during the period of time and both feet touching the ground; for b - foot And in the air, continues to rely; for with - again both feet touching the ground. The faster the walk, the shorter becomes the intervals a, C (cf. with the schedule runs, the last picture).

He can stay in this rather tedious position. But if he wants to go further, then tilts his body even more forward, moves the perpendicular from the centre of gravity outside the area of support and in danger of falling again puts forward leg, but not left and right - a new step, and so on the Walk so there is not that other, as the number of falls forward, warn delivered on time support legs that remained before behind.

As the man runs. A consistent body position when running (there are times when both legs are without support.

Let us consider the matter a little closer. Assume that the first step is taken. At this point the right foot even touches the ground, and the left is already set foot on the ground.

A graphical representation of the movement of the legs in running

From the graph we see that man running there are times (b, d, f), when both legs hovering in the air. This differs running from walking.

But only if the step is not very short, the right heel had to get up, because it is the lifting of the heel and allows the body to bend forward and to upset the balance. Left foot steps on the ground first with the heel. When after all the border of it on the earth becomes, the right leg is lifted completely in the air. At the same time the left leg, slightly bent at the knee straightens reduction of triceps thigh muscles and becomes momentarily vertical. This allows the bent right leg to move forward, not touching the ground, and to follow the movement of the body, to put on the ground his heel just in time for the next step.

A similar number of movements begins then to the left leg, which at this time is based on land only fingers and soon to go on air.

Running differs from walking to the fact that the foot is standing on the ground, the sudden contraction of her muscles vigorously drawn, and discards the body forward, so that last one moment completely separated from the earth. Then it drops again to land on the other leg, which, while the body was in the air quickly moved forward. Thus, the run consists of a series of jumps from one foot to another.

As for the energy spent by a person when walking on a horizontal road, it is not equal to Kul as some people think, the center of gravity of the human body with every step raised a few inches. It is possible to calculate that the work while walking along the horizontal path is about one fifteenth share the work of raising the human body to a height equal to the passed way.

Entertaining physics J. Perelman


System Orphus


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